
/*  -----------------------------------------------------------------------------------------------
    Namespace
--------------------------------------------------------------------------------------------------- */

var datoutiao = datoutiao || {};

// Set a default value for scrolled.
datoutiao.scrolled = 0;

// polyfill closest
// https://developer.mozilla.org/en-US/docs/Web/API/Element/closest#Polyfill
if ( ! Element.prototype.closest ) {
    Element.prototype.closest = function( s ) {
        var el = this;

        do {
            if ( el.matches( s ) ) {
                return el;
            }

            el = el.parentElement || el.parentNode;
        } while ( el !== null && el.nodeType === 1 );

        return null;
    };
}

// polyfill forEach
// https://developer.mozilla.org/en-US/docs/Web/API/NodeList/forEach#Polyfill
if ( window.NodeList && ! NodeList.prototype.forEach ) {
    NodeList.prototype.forEach = function( callback, thisArg ) {
        var i;
        var len = this.length;

        thisArg = thisArg || window;

        for ( i = 0; i < len; i++ ) {
            callback.call( thisArg, this[ i ], i, this );
        }
    };
}

// event "polyfill"
datoutiao.createEvent = function( eventName ) {
    var event;
    if ( typeof window.Event === 'function' ) {
        event = new Event( eventName );
    } else {
        event = document.createEvent( 'Event' );
        event.initEvent( eventName, true, false );
    }
    return event;
};

// matches "polyfill"
// https://developer.mozilla.org/es/docs/Web/API/Element/matches
if ( ! Element.prototype.matches ) {
    Element.prototype.matches =
        Element.prototype.matchesSelector ||
        Element.prototype.mozMatchesSelector ||
        Element.prototype.msMatchesSelector ||
        Element.prototype.oMatchesSelector ||
        Element.prototype.webkitMatchesSelector ||
        function( s ) {
            var matches = ( this.document || this.ownerDocument ).querySelectorAll( s ),
                i = matches.length;
            while ( --i >= 0 && matches.item( i ) !== this ) {}
            return i > -1;
        };
}

// Add a class to the body for when touch is enabled for browsers that don't support media queries
// for interaction media features. Adapted from <https://codepen.io/Ferie/pen/vQOMmO>.
datoutiao.touchEnabled = {

    init: function() {
        var matchMedia = function() {
            // Include the 'heartz' as a way to have a non-matching MQ to help terminate the join. See <https://git.io/vznFH>.
            var prefixes = [ '-webkit-', '-moz-', '-o-', '-ms-' ];
            var query = [ '(', prefixes.join( 'touch-enabled),(' ), 'heartz', ')' ].join( '' );
            return window.matchMedia && window.matchMedia( query ).matches;
        };

        if ( ( 'ontouchstart' in window ) || ( window.DocumentTouch && document instanceof window.DocumentTouch ) || matchMedia() ) {
            document.body.classList.add( 'touch-enabled' );
        }
    }
}; // datoutiao.touchEnabled

/*  -----------------------------------------------------------------------------------------------
    Cover Modals
--------------------------------------------------------------------------------------------------- */

datoutiao.coverModals = {

    init: function() {
        if ( document.querySelector( '.cover-modal' ) ) {
            // Handle cover modals when they're toggled.
            this.onToggle();

            // When toggled, untoggle if visitor clicks on the wrapping element of the modal.
            this.outsideUntoggle();

            // Close on escape key press.
            this.closeOnEscape();

            // Hide and show modals before and after their animations have played out.
            this.hideAndShowModals();
        }
    },

    // Handle cover modals when they're toggled.
    onToggle: function() {
        document.querySelectorAll( '.cover-modal' ).forEach( function( element ) {
            element.addEventListener( 'toggled', function( event ) {
                var modal = event.target,
                    body = document.body;

                if ( modal.classList.contains( 'active' ) ) {
                    body.classList.add( 'showing-modal' );
                } else {
                    body.classList.remove( 'showing-modal' );
                    body.classList.add( 'hiding-modal' );

                    // Remove the hiding class after a delay, when animations have been run.
                    setTimeout( function() {
                        body.classList.remove( 'hiding-modal' );
                    }, 500 );
                }
            } );
        } );
    },

    // Close modal on outside click.
    outsideUntoggle: function() {
        document.addEventListener( 'click', function( event ) {
            var target = event.target;
            var modal = document.querySelector( '.cover-modal.active' );

            // if target onclick is <a> with # within the href attribute
            if ( event.target.tagName.toLowerCase() === 'a' && event.target.hash.includes( '#' ) && modal !== null ) {
                // untoggle the modal
                this.untoggleModal( modal );
                // wait 550 and scroll to the anchor
                setTimeout( function() {
                    var anchor = document.getElementById( event.target.hash.slice( 1 ) );
                    anchor.scrollIntoView();
                }, 550 );
            }

            if ( target === modal ) {
                this.untoggleModal( target );
            }
        }.bind( this ) );
    },

    // Close modal on escape key press.
    closeOnEscape: function() {
        document.addEventListener( 'keydown', function( event ) {
            if ( event.keyCode === 27 ) {
                event.preventDefault();
                document.querySelectorAll( '.cover-modal.active' ).forEach( function( element ) {
                    this.untoggleModal( element );
                }.bind( this ) );
            }
        }.bind( this ) );
    },

    // Hide and show modals before and after their animations have played out.
    hideAndShowModals: function() {
        var _doc = document,
            _win = window,
            modals = _doc.querySelectorAll( '.cover-modal' ),
            htmlStyle = _doc.documentElement.style,
            adminBar = _doc.querySelector( '#wpadminbar' );

        function getAdminBarHeight( negativeValue ) {
            var height,
                currentScroll = _win.pageYOffset;

            if ( adminBar ) {
                height = currentScroll + adminBar.getBoundingClientRect().height;

                return negativeValue ? -height : height;
            }

            return currentScroll === 0 ? 0 : -currentScroll;
        }

        function htmlStyles() {
            var overflow = _win.innerHeight > _doc.documentElement.getBoundingClientRect().height;

            return {
                'overflow-y': overflow ? 'hidden' : 'scroll',
                position: 'fixed',
                width: '100%',
                top: getAdminBarHeight( true ) + 'px',
                left: 0
            };
        }

        // Show the modal.
        modals.forEach( function( modal ) {
            modal.addEventListener( 'toggle-target-before-inactive', function( event ) {
                var styles = htmlStyles(),
                    offsetY = _win.pageYOffset,
                    paddingTop = ( Math.abs( getAdminBarHeight() ) - offsetY ) + 'px',
                    mQuery = _win.matchMedia( '(max-width: 600px)' );

                if ( event.target !== modal ) {
                    return;
                }

                Object.keys( styles ).forEach( function( styleKey ) {
                    htmlStyle.setProperty( styleKey, styles[ styleKey ] );
                } );

                _win.datoutiao.scrolled = parseInt( styles.top, 10 );

                if ( adminBar ) {
                    _doc.body.style.setProperty( 'padding-top', paddingTop );

                    if ( mQuery.matches ) {
                        if ( offsetY >= getAdminBarHeight() ) {
                            modal.style.setProperty( 'top', 0 );
                        } else {
                            modal.style.setProperty( 'top', ( getAdminBarHeight() - offsetY ) + 'px' );
                        }
                    }
                }

                modal.classList.add( 'show-modal' );
            } );

            // Hide the modal after a delay, so animations have time to play out.
            modal.addEventListener( 'toggle-target-after-inactive', function( event ) {
                if ( event.target !== modal ) {
                    return;
                }

                setTimeout( function() {
                    var clickedEl = datoutiao.toggles.clickedEl;

                    modal.classList.remove( 'show-modal' );

                    Object.keys( htmlStyles() ).forEach( function( styleKey ) {
                        htmlStyle.removeProperty( styleKey );
                    } );

                    if ( adminBar ) {
                        _doc.body.style.removeProperty( 'padding-top' );
                        modal.style.removeProperty( 'top' );
                    }

                    if ( clickedEl !== false ) {
                        clickedEl.focus();
                        clickedEl = false;
                    }

                    _win.scrollTo( 0, Math.abs( _win.datoutiao.scrolled + getAdminBarHeight() ) );

                    _win.datoutiao.scrolled = 0;
                }, 500 );
            } );
        } );
    },

    // Untoggle a modal.
    untoggleModal: function( modal ) {
        var modalTargetClass,
            modalToggle = false;

        // If the modal has specified the string (ID or class) used by toggles to target it, untoggle the toggles with that target string.
        // The modal-target-string must match the string toggles use to target the modal.
        if ( modal.dataset.modalTargetString ) {
            modalTargetClass = modal.dataset.modalTargetString;

            modalToggle = document.querySelector( '*[data-toggle-target="' + modalTargetClass + '"]' );
        }

        // If a modal toggle exists, trigger it so all of the toggle options are included.
        if ( modalToggle ) {
            modalToggle.click();

            // If one doesn't exist, just hide the modal.
        } else {
            modal.classList.remove( 'active' );
        }
    }

}; // datoutiao.coverModals

/*  -----------------------------------------------------------------------------------------------
    Intrinsic Ratio Embeds
--------------------------------------------------------------------------------------------------- */

datoutiao.intrinsicRatioVideos = {

    init: function() {
        this.makeFit();

        window.addEventListener( 'resize', function() {
            this.makeFit();
        }.bind( this ) );
    },

    makeFit: function() {
        document.querySelectorAll( 'iframe, object, video' ).forEach( function( video ) {
            var ratio, iTargetWidth,
                container = video.parentNode;

            // Skip videos we want to ignore.
            if ( video.classList.contains( 'intrinsic-ignore' ) || video.parentNode.classList.contains( 'intrinsic-ignore' ) ) {
                return true;
            }

            if ( ! video.dataset.origwidth ) {
                // Get the video element proportions.
                video.setAttribute( 'data-origwidth', video.width );
                video.setAttribute( 'data-origheight', video.height );
            }

            iTargetWidth = container.offsetWidth;

            // Get ratio from proportions.
            ratio = iTargetWidth / video.dataset.origwidth;

            // Scale based on ratio, thus retaining proportions.
            video.style.width = iTargetWidth + 'px';
            video.style.height = ( video.dataset.origheight * ratio ) + 'px';
        } );
    }

}; // datoutiao.instrinsicRatioVideos

/*  -----------------------------------------------------------------------------------------------
    Modal Menu
--------------------------------------------------------------------------------------------------- */
datoutiao.modalMenu = {

    init: function() {
        // If the current menu item is in a sub level, expand all the levels higher up on load.
        this.expandLevel();
        this.keepFocusInModal();
    },

    expandLevel: function() {
        var modalMenus = document.querySelectorAll( '.modal-menu' );

        modalMenus.forEach( function( modalMenu ) {
            var activeMenuItem = modalMenu.querySelector( '.current-menu-item' );

            if ( activeMenuItem ) {
                datoutiaoFindParents( activeMenuItem, 'li' ).forEach( function( element ) {
                    var subMenuToggle = element.querySelector( '.sub-menu-toggle' );
                    if ( subMenuToggle ) {
                        datoutiao.toggles.performToggle( subMenuToggle, true );
                    }
                } );
            }
        } );
    },

    keepFocusInModal: function() {
        var _doc = document;

        _doc.addEventListener( 'keydown', function( event ) {
            var toggleTarget, modal, selectors, elements, menuType, bottomMenu, activeEl, lastEl, firstEl, tabKey, shiftKey,
                clickedEl = datoutiao.toggles.clickedEl;

            if ( clickedEl && _doc.body.classList.contains( 'showing-modal' ) ) {
                toggleTarget = clickedEl.dataset.toggleTarget;
                selectors = 'input, a, button';
                modal = _doc.querySelector( toggleTarget );

                elements = modal.querySelectorAll( selectors );
                elements = Array.prototype.slice.call( elements );

                if ( '.menu-modal' === toggleTarget ) {
                    menuType = window.matchMedia( '(min-width: 1000px)' ).matches;
                    menuType = menuType ? '.expanded-menu' : '.mobile-menu';

                    elements = elements.filter( function( element ) {
                        return null !== element.closest( menuType ) && null !== element.offsetParent;
                    } );

                    elements.unshift( _doc.querySelector( '.close-nav-toggle' ) );

                    bottomMenu = _doc.querySelector( '.menu-bottom > nav' );

                    if ( bottomMenu ) {
                        bottomMenu.querySelectorAll( selectors ).forEach( function( element ) {
                            elements.push( element );
                        } );
                    }
                }

                lastEl = elements[ elements.length - 1 ];
                firstEl = elements[0];
                activeEl = _doc.activeElement;
                tabKey = event.keyCode === 9;
                shiftKey = event.shiftKey;

                if ( ! shiftKey && tabKey && lastEl === activeEl ) {
                    event.preventDefault();
                    firstEl.focus();
                }

                if ( shiftKey && tabKey && firstEl === activeEl ) {
                    event.preventDefault();
                    lastEl.focus();
                }
            }
        } );
    }
}; // datoutiao.modalMenu

/*  -----------------------------------------------------------------------------------------------
    Primary Menu
--------------------------------------------------------------------------------------------------- */

datoutiao.primaryMenu = {

    init: function() {
        this.focusMenuWithChildren();
    },

    // The focusMenuWithChildren() function implements Keyboard Navigation in the Primary Menu
    // by adding the '.focus' class to all 'li.menu-item-has-children' when the focus is on the 'a' element.
    focusMenuWithChildren: function() {
        // Get all the link elements within the primary menu.
        var links, i, len,
            menu = document.querySelector( '.primary-menu-wrapper' );

        if ( ! menu ) {
            return false;
        }

        links = menu.getElementsByTagName( 'a' );

        // Each time a menu link is focused or blurred, toggle focus.
        for ( i = 0, len = links.length; i < len; i++ ) {
            links[i].addEventListener( 'focus', toggleFocus, true );
            links[i].addEventListener( 'blur', toggleFocus, true );
        }

        //Sets or removes the .focus class on an element.
        function toggleFocus() {
            var self = this;

            // Move up through the ancestors of the current link until we hit .primary-menu.
            while ( -1 === self.className.indexOf( 'primary-menu' ) ) {
                // On li elements toggle the class .focus.
                if ( 'li' === self.tagName.toLowerCase() ) {
                    if ( -1 !== self.className.indexOf( 'focus' ) ) {
                        self.className = self.className.replace( ' focus', '' );
                    } else {
                        self.className += ' focus';
                    }
                }
                self = self.parentElement;
            }
        }
    }
}; // datoutiao.primaryMenu

/*  -----------------------------------------------------------------------------------------------
    Toggles
--------------------------------------------------------------------------------------------------- */

datoutiao.toggles = {

    clickedEl: false,

    init: function() {
        // Do the toggle.
        this.toggle();

        // Check for toggle/untoggle on resize.
        this.resizeCheck();

        // Check for untoggle on escape key press.
        this.untoggleOnEscapeKeyPress();
    },

    performToggle: function( element, instantly ) {
        var target, timeOutTime, classToToggle,
            self = this,
            _doc = document,
            // Get our targets.
            toggle = element,
            targetString = toggle.dataset.toggleTarget,
            activeClass = 'active';

        // Elements to focus after modals are closed.
        if ( ! _doc.querySelectorAll( '.show-modal' ).length ) {
            self.clickedEl = _doc.activeElement;
        }

        if ( targetString === 'next' ) {
            target = toggle.nextSibling;
        } else {
            target = _doc.querySelector( targetString );
        }

        // Trigger events on the toggle targets before they are toggled.
        if ( target.classList.contains( activeClass ) ) {
            target.dispatchEvent( datoutiao.createEvent( 'toggle-target-before-active' ) );
        } else {
            target.dispatchEvent( datoutiao.createEvent( 'toggle-target-before-inactive' ) );
        }

        // Get the class to toggle, if specified.
        classToToggle = toggle.dataset.classToToggle ? toggle.dataset.classToToggle : activeClass;

        // For cover modals, set a short timeout duration so the class animations have time to play out.
        timeOutTime = 0;

        if ( target.classList.contains( 'cover-modal' ) ) {
            timeOutTime = 10;
        }

        setTimeout( function() {
            var focusElement,
                subMenued = target.classList.contains( 'sub-menu' ),
                newTarget = subMenued ? toggle.closest( '.menu-item' ).querySelector( '.sub-menu' ) : target,
                duration = toggle.dataset.toggleDuration;

            // Toggle the target of the clicked toggle.
            if ( toggle.dataset.toggleType === 'slidetoggle' && ! instantly && duration !== '0' ) {
                datoutiaoMenuToggle( newTarget, duration );
            } else {
                newTarget.classList.toggle( classToToggle );
            }

            // If the toggle target is 'next', only give the clicked toggle the active class.
            if ( targetString === 'next' ) {
                toggle.classList.toggle( activeClass );
            } else if ( target.classList.contains( 'sub-menu' ) ) {
                toggle.classList.toggle( activeClass );
            } else {
                // If not, toggle all toggles with this toggle target.
                _doc.querySelector( '*[data-toggle-target="' + targetString + '"]' ).classList.toggle( activeClass );
            }

            // Toggle aria-expanded on the toggle.
            datoutiaoToggleAttribute( toggle, 'aria-expanded', 'true', 'false' );

            if ( self.clickedEl && -1 !== toggle.getAttribute( 'class' ).indexOf( 'close-' ) ) {
                datoutiaoToggleAttribute( self.clickedEl, 'aria-expanded', 'true', 'false' );
            }

            // Toggle body class.
            if ( toggle.dataset.toggleBodyClass ) {
                _doc.body.classList.toggle( toggle.dataset.toggleBodyClass );
            }

            // Check whether to set focus.
            if ( toggle.dataset.setFocus ) {
                focusElement = _doc.querySelector( toggle.dataset.setFocus );

                if ( focusElement ) {
                    if ( target.classList.contains( activeClass ) ) {
                        focusElement.focus();
                    } else {
                        focusElement.blur();
                    }
                }
            }

            // Trigger the toggled event on the toggle target.
            target.dispatchEvent( datoutiao.createEvent( 'toggled' ) );

            // Trigger events on the toggle targets after they are toggled.
            if ( target.classList.contains( activeClass ) ) {
                target.dispatchEvent( datoutiao.createEvent( 'toggle-target-after-active' ) );
            } else {
                target.dispatchEvent( datoutiao.createEvent( 'toggle-target-after-inactive' ) );
            }
        }, timeOutTime );
    },

    // Do the toggle.
    toggle: function() {
        var self = this;

        document.querySelectorAll( '*[data-toggle-target]' ).forEach( function( element ) {
            element.addEventListener( 'click', function( event ) {
                event.preventDefault();
                self.performToggle( element );
            } );
        } );
    },

    // Check for toggle/untoggle on screen resize.
    resizeCheck: function() {
        if ( document.querySelectorAll( '*[data-untoggle-above], *[data-untoggle-below], *[data-toggle-above], *[data-toggle-below]' ).length ) {
            window.addEventListener( 'resize', function() {
                var winWidth = window.innerWidth,
                    toggles = document.querySelectorAll( '.toggle' );

                toggles.forEach( function( toggle ) {
                    var unToggleAbove = toggle.dataset.untoggleAbove,
                        unToggleBelow = toggle.dataset.untoggleBelow,
                        toggleAbove = toggle.dataset.toggleAbove,
                        toggleBelow = toggle.dataset.toggleBelow;

                    // If no width comparison is set, continue.
                    if ( ! unToggleAbove && ! unToggleBelow && ! toggleAbove && ! toggleBelow ) {
                        return;
                    }

                    // If the toggle width comparison is true, toggle the toggle.
                    if (
                        ( ( ( unToggleAbove && winWidth > unToggleAbove ) ||
                            ( unToggleBelow && winWidth < unToggleBelow ) ) &&
                            toggle.classList.contains( 'active' ) ) ||
                        ( ( ( toggleAbove && winWidth > toggleAbove ) ||
                            ( toggleBelow && winWidth < toggleBelow ) ) &&
                            ! toggle.classList.contains( 'active' ) )
                    ) {
                        toggle.click();
                    }
                } );
            } );
        }
    },

    // Close toggle on escape key press.
    untoggleOnEscapeKeyPress: function() {
        document.addEventListener( 'keyup', function( event ) {
            if ( event.key === 'Escape' ) {
                document.querySelectorAll( '*[data-untoggle-on-escape].active' ).forEach( function( element ) {
                    if ( element.classList.contains( 'active' ) ) {
                        element.click();
                    }
                } );
            }
        } );
    }

}; // datoutiao.toggles

/**
 * Is the DOM ready?
 *
 * This implementation is coming from https://gomakethings.com/a-native-javascript-equivalent-of-jquerys-ready-method/
 *
 * @param {Function} fn Callback function to run.
 */
function datoutiaoDomReady( fn ) {
    if ( typeof fn !== 'function' ) {
        return;
    }

    if ( document.readyState === 'interactive' || document.readyState === 'complete' ) {
        return fn();
    }

    document.addEventListener( 'DOMContentLoaded', fn, false );
}

datoutiaoDomReady( function() {
    datoutiao.toggles.init();              // Handle toggles.
    datoutiao.coverModals.init();          // Handle cover modals.
    datoutiao.intrinsicRatioVideos.init(); // Retain aspect ratio of videos on window resize.
    datoutiao.modalMenu.init();            // Modal Menu.
    datoutiao.primaryMenu.init();          // Primary Menu.
    datoutiao.touchEnabled.init();         // Add class to body if device is touch-enabled.
} );

/*  -----------------------------------------------------------------------------------------------
    Helper functions
--------------------------------------------------------------------------------------------------- */

/* Toggle an attribute ----------------------- */

function datoutiaoToggleAttribute( element, attribute, trueVal, falseVal ) {
    if ( trueVal === undefined ) {
        trueVal = true;
    }
    if ( falseVal === undefined ) {
        falseVal = false;
    }
    if ( element.getAttribute( attribute ) !== trueVal ) {
        element.setAttribute( attribute, trueVal );
    } else {
        element.setAttribute( attribute, falseVal );
    }
}

/**
 * Toggle a menu item on or off.
 *
 * @param {HTMLElement} target
 * @param {number} duration
 */
function datoutiaoMenuToggle( target, duration ) {
    var initialParentHeight, finalParentHeight, menu, menuItems, transitionListener,
        initialPositions = [],
        finalPositions = [];

    if ( ! target ) {
        return;
    }

    menu = target.closest( '.menu-wrapper' );

    // Step 1: look at the initial positions of every menu item.
    menuItems = menu.querySelectorAll( '.menu-item' );

    menuItems.forEach( function( menuItem, index ) {
        initialPositions[ index ] = { x: menuItem.offsetLeft, y: menuItem.offsetTop };
    } );
    initialParentHeight = target.parentElement.offsetHeight;

    target.classList.add( 'toggling-target' );

    // Step 2: toggle target menu item and look at the final positions of every menu item.
    target.classList.toggle( 'active' );

    menuItems.forEach( function( menuItem, index ) {
        finalPositions[ index ] = { x: menuItem.offsetLeft, y: menuItem.offsetTop };
    } );
    finalParentHeight = target.parentElement.offsetHeight;

    // Step 3: close target menu item again.
    // The whole process happens without giving the browser a chance to render, so it's invisible.
    target.classList.toggle( 'active' );

    /*
     * Step 4: prepare animation.
     * Position all the items with absolute offsets, at the same starting position.
     * Shouldn't result in any visual changes if done right.
     */
    menu.classList.add( 'is-toggling' );
    target.classList.toggle( 'active' );
    menuItems.forEach( function( menuItem, index ) {
        var initialPosition = initialPositions[ index ];
        if ( initialPosition.y === 0 && menuItem.parentElement === target ) {
            initialPosition.y = initialParentHeight;
        }
        menuItem.style.transform = 'translate(' + initialPosition.x + 'px, ' + initialPosition.y + 'px)';
    } );

    /*
     * The double rAF is unfortunately needed, since we're toggling CSS classes, and
     * the only way to ensure layout completion here across browsers is to wait twice.
     * This just delays the start of the animation by 2 frames and is thus not an issue.
     */
    requestAnimationFrame( function() {
        requestAnimationFrame( function() {
            /*
             * Step 5: start animation by moving everything to final position.
             * All the layout work has already happened, while we were preparing for the animation.
             * The animation now runs entirely in CSS, using cheap CSS properties (opacity and transform)
             * that don't trigger the layout or paint stages.
             */
            menu.classList.add( 'is-animating' );
            menuItems.forEach( function( menuItem, index ) {
                var finalPosition = finalPositions[ index ];
                if ( finalPosition.y === 0 && menuItem.parentElement === target ) {
                    finalPosition.y = finalParentHeight;
                }
                if ( duration !== undefined ) {
                    menuItem.style.transitionDuration = duration + 'ms';
                }
                menuItem.style.transform = 'translate(' + finalPosition.x + 'px, ' + finalPosition.y + 'px)';
            } );
            if ( duration !== undefined ) {
                target.style.transitionDuration = duration + 'ms';
            }
        } );

        // Step 6: finish toggling.
        // Remove all transient classes when the animation ends.
        transitionListener = function() {
            menu.classList.remove( 'is-animating' );
            menu.classList.remove( 'is-toggling' );
            target.classList.remove( 'toggling-target' );
            menuItems.forEach( function( menuItem ) {
                menuItem.style.transform = '';
                menuItem.style.transitionDuration = '';
            } );
            target.style.transitionDuration = '';
            target.removeEventListener( 'transitionend', transitionListener );
        };

        target.addEventListener( 'transitionend', transitionListener );
    } );
}

/**
 * Traverses the DOM up to find elements matching the query.
 *
 * @param {HTMLElement} target
 * @param {string} query
 * @return {NodeList} parents matching query
 */
function datoutiaoFindParents( target, query ) {
    var parents = [];

    // Recursively go up the DOM adding matches to the parents array.
    function traverse( item ) {
        var parent = item.parentNode;
        if ( parent instanceof HTMLElement ) {
            if ( parent.matches( query ) ) {
                parents.push( parent );
            }
            traverse( parent );
        }
    }

    traverse( target );

    return parents;
}
